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Modelling nutritional effects on reproduction in dairy cows - AC0218

Dairy systems account for 40% of UK agricultural methane emissions, the majority of which (80%) arise from enteric fermentation in the rumen. Total methane emissions at farm or national level are the product of number of cows and emissions per cow. It is easy to count cows, but conventional methods cannot measure methane emissions accurately in dairy cows kept under commercial conditions. This presents a problem for evaluating potential mitigation strategies. We have developed a novel technique to provide individual methane emissions, based on continuous real-time analysis of methane in breath samples taken during milking in a robotic system.

Preliminary observations of 40 cows showed large increases in breath methane concentration following eructation. Mean eructation interval per cow varied from 45 to 85 seconds and peak methane concentration varied between 800 and 7000 ppm. Importantly, both peak interval and concentration were consistent within cows and both were related to milk yield. The relationships were consistent with daily methane outputs predicted by published equations derived from cows in respiration chambers.

Clearly, the ability to measure eructation rate and peak methane concentration in real time represents a significant advance in methodology. These parameters indicate physiological processes that determine daily methane emissions and it is easy to replicate measurements to provide robust estimates for individuals. We propose to use this technique to monitor methane emissions from at least 200 individual cows up to three times daily at intervals over a 6-month period. This will show between animal variations to see if selection for low methane producers is likely to be beneficial.

To give greater confidence in the new technique, measurements will be calibrated against two conventional techniques. Respiration chambers are used to provide accurate measures of total daily emissions by individual cows. The tracer technique involving sulphur hexafluoride is used to estimate daily emissions by group-housed individual cows. During calibration against these techniques, cows will be fed on diets known to affect methane production. Data will be analysed for relationships between methane emissions and milk yield, feed intake and composition, stage of lactation and season. Relationships will be compared with published equations and predictions.

The objectives of the project are:
Objective 1 – to collect data on methane emissions by 200 individual cows during milking, which will indicate variation among cows and relationships between methane and production parameters.
Objective 2 – to calibrate the technique against methane measurements made with respiration chambers and tracer techniques.
Objective 3 – to compare methane measurements made under Objectives 1 and 2 with predictions from published models.

This work will provide, for the first time, quantitative estimates of the scope for reducing methane emissions through genetic selection and altering management practices. Importantly, the data will be generated from lactating cows housed under commercial conditions and will be considerably more realistic than extrapolations from sheep or from cows housed in respiration chambers. This will provide researchers and advisors with more reliable data for building and testing prediction models of methane emissions. If a significant genetic effect on methane emissions is confirmed in subsequent studies, this offers opportunities for long-term cumulative and permanent reductions through selection programmes. If genetic markers for methane emissions can be identified in subsequent studies, they will offer the opportunity for accelerated genetic progress. This project will therefore provide Defra policy makers with vital evidence and tools to assist delivery of pledges made in the Climate Change Programme.
The aim of this project is to produce a modelling framework that links nutrition, metabolism and reproduction of dairy cows in a predictive manner using dynamic, mechanistic models. The framework will simulate physiological processes and control mechanisms, based initially on published models that describe elements of the relevant systems together with data available from our previous studies. The structure will be modular to facilitate subsequent development when more detailed or novel information becomes available, and to permit validation of individual pathways as well as overall predictions.

To address this aim, the objectives of the project are:
1. To review available mathematical models and select those that meet our requirements
2. To convert equations from selected models into standard format and units
3. To combine these equations into integrated modules and test initial model predictions against available data
4. To identify significant gaps and critical control points requiring further development

Because the duration of the project is only 6 months, it is not appropriate to allocate a shorter timescale to any individual objective. All objectives will be ongoing and concurrent throughout the project period, with a milestone of 6 months.
Project Documents
• Final Report : Modelling Nutritional Effects on Reproduction in Dairy Cows   (695k)
• Summary Report : Modelling nutritional effects on reproduction in dairy cows   (38k)
Time-Scale and Cost
From: 2009

To: 2010

Cost: £76,764
Contractor / Funded Organisations
University - Nottingham
Agriculture and Climate Change              
Renewable materials              
Sustainable Farming and Food Science              
Fields of Study
Agriculture and Climate Change